The device shown in FIG. 18 is a known power conversion device of the above kind. This power conversion device compensates for 3-phase alternating current power supply voltage fluctuation, and supplies a stable 3-phase alternating current voltage to a load. The power conversion device is such that a 3-phase alternating current power supply and a load are V-connected, and a predetermined 3-phase alternating current voltage is generated using the voltage of the 3-phase alternating current power supply and a direct current voltage generated from this voltage.
In the drawing, 1 is a 3-phase alternating current power supply, 21 and 22 are capacitors, 3u and 3w are converter circuits, 4u and 4w are inverter circuits, 5 is a filter circuit, 6 is a 3-phase load, and K1 to K3 are switching means.
The 3-phase alternating current power supply 1 includes terminals R, S, and T that output an R-phase, S-phase, and T-phase voltage. The capacitor 21 is connected between the terminal R and terminal S of the 3-phase alternating current power supply 1. The capacitor 22 is connected between the terminal S and terminal T of the 3-phase alternating current power supply 1.
The converter circuit 3u has as main components a circuit wherein switching elements Qu and Qx are connected in series, a circuit wherein capacitors Cpu and Cnu are connected in series, a bidirectional switch element Su, and a reactor Lu. The series circuit of the switching elements Qu and Qx is connected in parallel with the series circuit of the capacitors Cpu and Cnu. A connection point of the capacitor Cpu and capacitor Cnu is connected via the switching means K1 to the terminal R of the 3-phase alternating current power supply 1. One end of the capacitor Cnu is connected via the switching means K3 to the terminal S of the 3-phase alternating current power supply 1. The bidirectional switch element Su is connected between a connection point of the switching elements Qu and Qx and a connection point of the capacitors Cpu and Cnu. One end of the reactor Lu is connected to a connection point of the switching elements Qu and Qx, and the other end is connected via the switching means K3 to the terminal S of the 3-phase alternating current power supply 1.
A positive side terminal of the series circuit of the capacitors Cpu and Cnu is connected to a terminal Pu that outputs a positive voltage of the converter circuit 3u. A negative side terminal of the series circuit of the capacitors Cpu and Cnu is connected to a terminal Nu that outputs a negative voltage of the converter circuit 3u. A connection point of the capacitor Cpu and capacitor Cnu is connected to a terminal Ou that outputs a neutral point voltage of the converter circuit 3u. 
The inverter circuit 4u has as main components a circuit wherein switching elements Q1 and Q2 are connected in series and a bidirectional switch element S1. The series circuit of the switching elements Q1 and Q2 is connected to the terminal Pu and terminal Nu of the converter circuit 3u. The bidirectional switch element S1 is connected between a connection point of the switching elements Q1 and Q2 and the terminal Ou of the converter circuit 3u. A connection point of the switching elements Q1 and Q2 is connected to a terminal U, which is for the inverter circuit 4u to output an alternating current voltage.
The switching elements Q1 and Q2 and the bidirectional switch element S1 are configured of semiconductor elements, such as IGBTs (Insulated Gate Bipolar Transistors), such that a turn on/turn off operation can be carried out at a frequency that is sufficiently high with respect to the frequency of the 3-phase alternating current power supply 1.
The converter circuit 3w has as main components a circuit wherein switching elements Qw and Qz are connected in series, a circuit wherein capacitors Cpw and Cnw are connected in series, a bidirectional switch element Sw, and a reactor Lw. As the converter circuit 3w has a circuit configuration symmetrical to that of the converter circuit 3u across a line connecting the terminal S of the 3-phase alternating current power supply 1 and an alternating current output terminal V, a description of the connection relationship of each component will be omitted.
The inverter circuit 4w has as main components a circuit wherein switching elements Q3 and Q4 are connected in series and a bidirectional switch element S4. As the inverter circuit 4w too, in the same way, has a circuit configuration symmetrical to that of the inverter circuit 4u across a line connecting the terminal S of the 3-phase alternating current power supply 1 and the alternating current output terminal V, a description of the connection relationship of each component will be omitted. A connection point of the switching elements Q3 and Q4 is connected to a terminal W, which is for the inverter circuit 4w to output an alternating current voltage.
According to the heretofore described circuit configuration, the converter circuit 3u is such that each of the capacitors Cpu and Cnu is charged to an equal voltage using a line voltage Vrs between the terminal R and terminal S of the 3-phase alternating current power supply 1. Further, the converter circuit 3u maintains the voltage of the capacitors Cpu and Cnu at a predetermined voltage higher than the amplitude value of the line voltage Vrs.
The converter circuit 3u outputs a line voltage Vuv between the alternating current output terminals U and V, using the positive and negative voltages of the series circuit of the capacitors Cpu and Cnu and the neutral point voltage. The line voltage Vuv is a voltage that is the positive and negative voltages of the series circuit of the capacitors Cpu and Cnu superimposed on the line voltage Vrs. The fundamental waveform of the line voltage Vuv has a predetermined voltage amplitude in accordance with a voltage command.
In the same way, the converter circuit 3w is such that each of the capacitors Cpw and Cnw is charged to an equal voltage using a line voltage Vts between the terminal S and terminal T of the 3-phase alternating current power supply 1. Further, the converter circuit 3w maintains the voltage of the capacitors Cpw and Cnw at a voltage higher than the amplitude value of the line voltage Vts.
The converter circuit 3w outputs a line voltage Vwv between the alternating current output terminals V and W, using the positive and negative voltages of the series circuit of the capacitors Cpw and Cnw and the neutral point voltage. The line voltage Vwv is a voltage that is the positive and negative voltages of the series circuit of the capacitors Cpw and Cnw superimposed on the line voltage Vts. The fundamental waveform of the line voltage Vwv has a predetermined voltage amplitude in accordance with a voltage command. Also, the line voltage Vwv is regulated to a phase deviating 120 degrees with respect to the line voltage Vuv.
The power conversion device is such that the amount of voltage superimposed on the line voltages Vrs and Vts is adjusted when the voltage of the 3-phase alternating current power supply 1 fluctuates, thus maintaining the line voltages Vuv and Vwv at predetermined values.
Also, the power conversion device is such that the switching means K1 to K3 are opened when the 3-phase alternating current power supply 1 is interrupted. Also, the power conversion device operates so that predetermined line voltages Vuv and Vwv are output using the voltage of the series circuit of the capacitors Cpu and Cnu and the voltage of the series circuit of the capacitors Cpw and Cnw.
The heretofore described power conversion device is disclosed in JP-A-2012-44824.